NTFS does not support the permission system as required by Ubuntu. You can choose to share the NTFS drive for data among all OS, but you will either have to install Ubuntu using wubi, which is not recommended if you would like to use Ubuntu seriously, or make a separate partition that meets the minimum requirements.
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MaheshDec 14 '12 at 10:24

You would need to partition the disk in any case, so you may as well format the partition(s) for Ubuntu as normal (ext4 etc) and your NTFS data files will be accessible from within Ubuntu, but Windows won't see your Ubuntu data so you should consider where to store things that may need to be accessible from both i.e. put it on the NTFS (Windows) partition.

The installer will do the partitioning for you and give you dual boot if you choose the "Install alongside Windows" option.